Which laboratory study has the highest sensitivity for early onset sepsis?

• A. Immature neutrophil count
• B. Ratio of immature to total neutrophils
• C. Total neutrophil count
• D. C-reactive protein

Answer: (B)

In newborns, the earliest signs of sepsis often show up as a left shift in neutrophils—the bone marrow starts releasing immature forms (bands, metas, etc.) in response to infection. The immature-to-total neutrophil ratio captures this shift by measuring not just how many neutrophils are present, but what fraction are immature. That makes it more sensitive to early infection than looking at immature neutrophil count alone, because even when the total pool is normal or only mildly elevated, a rising proportion of immature cells signals an active marrow response. Total neutrophil count can be normal or even low in sepsis, so it’s not as reliable early on. C-reactive protein rises later as an acute-phase reactant, so it’s less sensitive in the very early phase. Thus, the immature-to-total neutrophil ratio best detects early onset sepsis.